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On 27/08/19 1:47 AM, Brian Rosmaita wrote:
> On 8/26/19 4:24 AM, Sean Mooney wrote:
>> On Mon, 2019-08-26 at 18:18 +1200, Jordan Ansell wrote:
>>> Hi Openstack Discuss,
>>>
>>> I have an issue with nova not synchronizing changes between a glance
>>> image and it's local image meta information in nova.
>>>
>>> I have updated a glance image with the property "hw_rng_model=virtio",
>>> and that successfully passes that to new instances created using the
>>> updated image. However existing instances do not receive this new property.
>>>
>>> I have located the image metadata within the nova database, in the
>>> **instance_system_metadata** table, and can see it's not updated for the
>>> existing instances, and only adding the relevant rows for instances that
>>> are created when that property is present. The key being
>>> "image_hw_rng_model" and "virtio" being the value.
>>>
>>> Is there a way to tell nova to update the table for existing instances,
>>> and synchronizing the two databases? Or is this the kind of thing that
>>> would need to be done *shudder* manually...?
>> this is idealy not something you would do at all.
>> nova create a local copy of the image metadata the instace was booted with
>> intionally to not pick up chagne you make to the image metadata after you boot
>> the instance. in some case those change could invalidate the host the image is on so
>> it in general in not considerd safe to just sync them
>>
>> for the random number generator it should be ok but if you were to add a trait requirement
>> of alter the numa topology then it could invalidate the host as a candiate for that instance.
>> so if you want to do this then you need to update it manually as nova is working as
>> intended by not syncing the data.
>>>  If so, are there any
>>> experts out there who can point me to some documentation on doing this
>>> correctly before I go butcher a couple of dummy nova database?
>> there is no docs for doing this as it is not a supported feature.
>> you are circumventing a safty feature we have in nova to prevent change to running instances
>> after they are first booted by change to the flavor extra spec or image metadata.
>>> Regards,
>>> Jordan
>>>
>>>
>>
> I agree with everything Sean says here.  I just want to remind you that
> if you use the nova image-create action on an instance, the image
> properties put on the new image are pulled from the nova database.  So
> if you do decide to update the DB manually (not that I am recommending
> that!), don't forget that any already existing snapshot images will have
> the "wrong" value for the property.  (You can update them via the Images
> API.)
>
Thanks Sean and Brian..!

I hadn't considered the snapshots.. that's a really good point! And
thank you for the warnings, I can see why this isn't something that's
synchronized automatically :S

Regards,
Jordan